The present invention generally relates to optical imaging systems, optical probes thereof, and methods thereof for providing images of spatial or temporal distribution of chromophores or their properties in various physiological media. More particularly, the present invention relates to optical imaging systems and/or optical probes thereof including symmetrically arranged optical sensors such as wave sources and/or detectors. The present invention is applicable to any optical imaging systems and/or optical probes thereof whose operation is based on wave equations including the Beer-Lambert equation, modified Beer-Lambert equation, photon diffusion equation, and their equivalents.
Near-infrared spectroscopy has been used to measure various physiological properties in animal and human subjects. The basic principle underlying the near-infrared spectroscopy is that a physiological medium such as tissues and cells includes a variety of light-absorbing and light-scattering chromophores which can interact with electromagnetic waves transmitted thereto and traveling therethrough. For example, human tissues include numerous chromophores among which deoxygenated and oxygenated hemoglobins are the most dominant chromophores in the spectrum range of 600 nm to 900 nm. Therefore, the near-infrared spectroscope has been applied to measure oxygen levels in the physiological medium in terms of tissue hemoglobin oxygen saturation (xe2x80x9coxygen saturationxe2x80x9d hereinafter). Technical background for the near-infrared spectroscopy and diffuse optical imaging has been discussed in, e.g., Neuman, M. R., xe2x80x9cPulse Oximetry: Physical Principles, Technical Realization and Present Limitations,xe2x80x9d Adv. Exp. Med. Biol., vol. 220, p.135-144, 1987, and Severinghaus, J. W., xe2x80x9cHistory and Recent Developments in Pulse Oximetry,xe2x80x9d Scan. J. Clin. and Lab. Investigations, vol. 53, p.105-111, 1993.
Various techniques have been developed for the near-infrared spectroscopy, including time-resolved spectroscopy (TRS), phase modulation spectroscopy (PMS), and continuous wave spectroscopy (CWS). In a homogeneous, semi-infinite model, the TRS and PMS have generally been used to solve the photon diffusion equation, to obtain the spectra of absorption coefficients and reduced scattering coefficients of the physiological medium, and to estimate concentrations of the oxygenated and deoxygenated hemoglobins and oxygen saturation. The CWS has generally been used to solve the modified Beer-Lambert equation and to calculate changes in the concentrations of the oxygenated and deoxygenated hemoglobins.
Despite their capability of providing hemoglobin concentrations as well as the oxygen saturation, the major disadvantage of the TRS and PMS is that the equipment has to be bulky and, therefore, expensive. The CWS may be manufactured at a lower cost but is generally limited in its utility, for it can estimate only the changes in the hemoglobin concentrations but not the absolute values thereof. Accordingly, the CWS cannot provide the oxygen saturation. The prior art technology also requires a priori calibration of optical probes before their clinical application by, e.g., measuring a baseline in a reference medium or in a homogeneous portion of the medium. Furthermore, all prior art technology requires complicated image reconstruction algorithms to generate images of two-dimensional and/or three-dimensional distribution of the chromophores or their properties.
Accordingly, there exist needs for more efficient and reliable optical imaging systems and optical probes thereof for measuring absolute values of chromophores or their properties, for calibrating signals and images from such systems and probes while obviating the need for separate calibration procedure, and for constructing the images of the foregoing distribution of the chromophores or their properties on a substantially real time basis.
The present invention generally relates to optical imaging systems, optical probes thereof, and methods therefor (collectively referred to as xe2x80x9coptical imaging systemxe2x80x9d or xe2x80x9coptical probexe2x80x9d hereinafter) for providing two-dimensional or three-dimensional images of spatial or temporal distribution of chromophores or their properties in various physiological media. More particularly, the present invention relates to the optical imaging systems that are equipped with optical probes incorporating symmetrically arranged wave sources and wave detectors.
In one aspect of the invention, an optical imaging system is provided for generating images of a target area of a physiological medium, where the images represent two- and/or three-dimensional spatial and/or temporal distribution of the chromophores or their properties in the target area of the medium. Such an optical imaging system typically includes at least one wave source arranged to form optical coupling with the physiological medium and to irradiate electromagnetic waves into the medium and at least one wave detector arranged to detect electromagnetic waves from the medium and to generate output signal in response thereto. The optical imaging system then groups the wave sources and detectors such that each pair of one wave source and one wave detector forms a scanning element in which the wave source irradiates electromagnetic waves into the target area of the medium and in which the wave detector detects the electromagnetic waves irradiated by the wave source and generates the output signal in response thereto. The optical imaging system also groups the wave sources and detectors (or groups multiple scanning elements themselves) in order to define multiple symmetric scanning units each of which includes at least two wave sources and at least two wave detectors such as a first wave source, second wave source, first wave detector, and second wave detector. The first wave source may be disposed closer to the first wave detector than the second wave detector, while the second wave source is disposed closer to the second wave detector than the first wave detector. The wave sources and detectors are also arranged so that a first near-distance between the first wave source and first wave detector is identical or substantially similar to a second near-distance between the second wave source and second wave detector. In addition, a first far-distance between the first wave source and the second wave detector is identical or substantially similar to a second far-distance between the second wave source and the first wave detector. The near-distance is preferably about one half of the far-distance but may also be arranged to be longer or shorter than one half of the far-distance.
Embodiments of this aspect of the present invention includes one or more of the following features.
The symmetric scanning unit may include an axis of symmetry such that the first and second wave sources are disposed symmetric to such axis and the first and second wave detectors are also disposed symmetric thereto. Multiple symmetric scanning units may be arranged to include at least one common wave source and/or at least one common wave detector.
The wave sources and detectors of such scanning units may be substantially linearly disposed so that the wave sources (or detectors) are interposed between the wave detectors (or sources). Two or more symmetric scanning units may share the common axis of symmetry, e.g., where the first scanning unit has a first source-detector arrangement and where the second scanning unit is disposed below the first scanning unit and has the same first arrangement or, in the alternative, has a second source-detector arrangement which is different from or substantially reverse to the first source-detector arrangement. In one embodiment, four symmetric scanning units may be arranged to share the common axis of symmetry, e.g., where the first scanning unit has a first source-detector arrangement, where the second scanning unit is disposed below the first scanning unit and has a second source-detector arrangement substantially reverse to the first arrangement, where the third scanning unit is disposed below the second scanning unit and has the second arrangement, and where the fourth scanning unit is disposed below the third scanning unit and has the first source-detector arrangement. The foregoing scanning units may have identical shapes and sizes and define a 4xc3x974 rectangular or square source-detector array so that adjacent wave sources and detectors are spaced apart by a uniform distance.
The wave sources and detectors may be disposed to form four vertices of a quadrangle, e.g., with the wave sources disposed at two upper vertices of the quadrangle while the wave detectors are disposed at two lower vertices thereof. Examples of such quadrangles include a square, rectangle, and trapezoid having two sides of equal lengths. Two or more of quadrangular scanning units may be arranged to have different sizes, to be disposed with respect to different axes of symmetry, and/or to have the same, different or reverse source-detector arrangements. Such quadrangular scanning units may be provided in various geometric arrangement, e.g., a side by side arrangement, stacked arrangement, arcuate arrangement or a combination thereof. For example, four quadrangular symmetric scanning units may be arranged so that the first scanning unit has a first source-detector arrangement, that the second scanning unit is disposed next to the first scanning unit and has a second source-detector arrangement which is substantially reverse to the first arrangement, that the third scanning unit is disposed below the first scanning unit and has the second arrangement, and that the fourth scanning unit is disposed below the second symmetric scanning unit and has the first arrangement. Alternatively, the first set of the wave sources and detectors may be substantially linearly disposed to define a linear scanning unit, while the second set of the wave sources and detectors may be disposed to form four vertices of such quadrangle and, therefore, to define an areal scanning unit. The first and second sets of the sensors may be arranged to include at least one common wave source and/or at least one common wave detector.
Alternatively, the symmetric scanning unit may include a point of symmetry so that the first and second wave sources are symmetrically disposed with respect to such point and the first and second wave detectors are also disposed symmetrically thereto. The symmetric scanning units may be arranged to include at least one common wave source and/or at least one common wave detector. The wave sources and detectors may also be substantially linearly disposed or may be disposed to form four vertices of a quadrangle, in which the first wave source and the first wave detector are disposed at two upper vertices of the quadrangle, while the second wave detector and the second wave source are disposed at two lower vertices thereof. Examples of such quadrangles may include, but not limited to, a rectangle and a parallelogram having two adjacent sides of different lengths (i.e., excluding a diamond-shaped parallelogram).
The symmetric scanning unit may also include one or more additional wave sources and/or detectors which may be disposed along a side, in a corner or in a middle portion of the scanning unit. In turn, the optical imaging system may include two or more symmetric scanning units arranged symmetrically with respect to a global axis of symmetry or a global point of symmetry in various arrangements, e.g., a side by side, stacked, angled, arcuate, and/or concentric arrangement. The symmetric scanning unit may also be arranged asymmetrically with respect to the other scanning units or to intersect and/or overlap other scanning units as well.
The wave sources may irradiate multiple sets of electromagnetic waves having different wave characteristics and the wave detectors may detect multiple sets of electromagnetic waves having different wave characteristics. In addition, the wave sources may be synchronized so that when one wave source is irradiating electromagnetic waves, other wave sources are turned off.
In another aspect of the invention, an optical imaging system includes four or more symmetric scanning units, where a first scanning unit is identical to a fourth scanning unit and where a second scanning unit is identical to a third scanning unit. Each symmetric scanning unit includes a first wave source, a second wave source, a first wave detector, and a second wave detector, where the first wave source is disposed closer to the first than the second wave detector and where the second wave source is disposed closer to the second than the first wave detector. The wave sources and detectors are arranged to render a first near-distance between the first wave source and first wave detector identical or substantially similar to a second near-distance between the second wave source and second wave detector and to render a first far-distance between the first wave source and second wave detector identical or substantially similar to a second far-distance between the second wave source and first wave detector. At least one of the first and second wave sources may be arranged to be synchronized with at least one of the first and second wave detectors so as to generate the output signals which represent optical interaction between the near-infrared waves and the hemoglobins in said target areas of said medium.
Embodiments of this aspect of the present invention includes one or more of the following features.
All wave sources and detectors of each scanning unit may be substantially linearly disposed. For example, the first and second wave sources (or detectors) may be interposed between the first and second wave detectors (or sources) in the first and fourth (or second and third) scanning units.
In yet another aspect of the present invention, an optical probe of an optical imaging system is provided to generate images representing distribution of chromophores or their properties in target areas of a physiological medium. Such an optical probe includes multiple wave sources and multiple wave detectors, where the wave sources are arranged to form optical coupling with the target areas of the medium and to irradiate electromagnetic waves thereinto, while the wave detectors are arranged to detect electromagnetic waves and to generate output signals in response thereto. In general, at least one first wave source and at least one first wave detector define a first scanning element in which the first wave source irradiates electromagnetic waves and in which the first wave detector detects such waves irradiated by the first wave detector and generates a first output signal. At least one second wave source and at least one second wave detector also define a second scanning element in which the second wave source irradiates electromagnetic waves and in which the second wave detector detects such waves irradiated by the second wave detector and generates a second output signal. The first and second scanning elements define a scanning unit in which the first and second wave sources are symmetrically disposed with respect to one of a line of symmetry and a point of symmetry and in each of which the first and second wave detectors are also symmetrically disposed with respect to one of the line of symmetry and the point of symmetry. Two or more of such scanning units may be arranged to intersect or overlap each other.
Embodiments of this aspect of the present invention includes one or more of the following features.
The optical probe may include an imaging member arranged to receive the first and second output signals generated by the first and second wave detectors, to obtain a set of solutions of multiple wave equations applied to the first and second wave sources and to the first and second wave detectors, to determine the distribution of the chromophores or their properties, and to generate the images of such distribution. Such images are generally provided in an image domain and are comprised of multiple voxels, where each of the first and second scanning units generates multiple first voxels as well as multiple second voxels, respectively. The imaging member is arranged to calculate at least one first voxel value for each of the first voxels from the set of solutions and at least one second voxel value for each of the second voxels from the same set of solutions. The imaging member is also arranged to define multiple cross-voxels each of which is defined as an overlapping portion of the first and second voxels intersecting each other.
The imaging member is also arranged to calculate at least one cross-voxel value for each of the cross-voxels directly from the first and second voxel values of the intersecting first and second voxels, respectively. Each of the cross-voxel values can be obtained as an arithmetic sum or arithmetic average of the first and second voxel values of the first and second voxels intersecting each other. Alternatively, each cross-voxel value may also be obtained at a weighted sum or weighted average of the first and second voxel values of the first and second voxels intersecting each other.
In a further aspect, a method is provided to generate the foregoing images of a target area of a physiological medium by an optical imaging system with an optical probe including the foregoing wave sources and detectors. The method generally includes the steps of providing multiple scanning elements each including at least one wave source for irradiating said waves and at least one wave detector for detecting such waves irradiated by the wave source of each of such scanning units, defining multiple scanning units each including at least two scanning elements and, therefore, each including at least two wave sources and detectors, scanning the target area by irradiating electromagnetic waves into such target area by the wave sources and by generating the output signals therefrom by the wave detectors, grouping such output signals generated by each scanning units, obtaining a set of solutions of wave equations applied to the wave sources and detectors of each of the scanning units, determining the distribution of the chromophores and/or properties thereof from the set of solutions, and providing the images of such distribution.
Embodiments of this aspect of the present invention includes one or more of the following features.
The method may include the steps of scanning said target area over a certain period of time, determining the distribution of the chromophores or properties thereof in the target area of the medium over time, providing the images of such distribution over time, and providing the images of changes in such distribution over time.
The method may also include the steps of defining a plurality of first voxels in at least one of the scanning units, determining at least one first voxel value for each of the first voxels, where each first voxel value represents an average value of the chromophores or their properties, generating the images of such distribution directly from the first voxel values. The method also includes the step of controlling resolution of the final images by adjusting at lease one characteristic dimension of each first voxel, e.g., by controlling the distance between the wave source and detector in one scanning element or unit, adjusting geometric arrangement between the wave source and wave detector in one scanning element or unit, adjusting geometric arrangement between multiple scanning elements in a scanning unit, adjusting geometric arrangement between at least two scanning units and adjusting a data sampling rate of the output signals.
The method may also include the steps of defining multiple second voxels in at least one scanning unit, determining at least one second voxel value for each second voxel where each second voxel value represents an average value of the chromophores or their properties, generating the images of such distribution directly from the first and second voxel values.
The method may include the steps of defining multiple cross-voxels in each scanning unit where the cross-voxel is defined as an overlapping portion of two or more intersecting first and second voxels, determining at least one cross-voxel value for each of the cross-voxels where each cross-voxel value is an average value of the chromophores or their properties, and generating the images of such distribution directly from the cross-voxel values, first voxel values, and second voxel values. The cross-voxel values are determined by, e.g., adding the first and second voxel values of the intersecting first and second voxels, arithmetically averaging the first and second voxel values of the intersecting first and second voxels, adding weighted first and second voxel values of the intersecting first and second voxels, and weight-averaging the first and second voxel values of the intersecting first and second voxels.
The method may also include the steps of defining multiple third voxels in the scanning units, determining one or more third voxel value for each of the third voxels where each third voxel value reflects an average value of at least one of the chromophores or their properties thereof, and generating the images of the distribution directly from the first, second, and third voxel values. In addition, the method may further include the steps of defining multiple second cross-voxels in the scanning units where each second cross-voxel is defined as an overlapping portion of two or more intersecting first and third voxels, determining at least one second cross-voxel value for each second cross-voxel where such second cross-voxel value reflects an average value of the chromophores or their properties, and generating the images of such distribution based on the cross-voxel values, second cross-voxel values, first voxel values, second voxel values, and third voxel values.
Each of the foregoing optical imaging systems and methods of the present invention may incorporate analytical and/or numerical solution schemes disclosed in the commonly assigned co-pending U.S. non-provisional patent application bearing Ser. No. 09/664,972, entitled xe2x80x9cA system and Method for Absolute Oxygen Saturationxe2x80x9d which has been filed on Sep. 18, 2000 by Xuefeng Cheng, Xiaorong Xu, Shuoming Zhou, and Ming Wang and which is incorporated herein by reference in its entirety (referred to as xe2x80x9cthe ""972 applicationxe2x80x9d hereinafter). Such optical imaging systems can calculate absolute values of concentration of oxygenated hemoglobin, [HbO], that of deoxygenated hemoglobin, [Hb], oxygen saturation, SO2, and temporal changes in blood volume or water by adopting any of the schemes disclosed in the co-pending ""972 application. Accordingly, such optical imaging systems provide the foregoing images of distribution of the chromophores and their properties that allow physicians to make direct diagnosis of the target area of the medium based on xe2x80x9cabsolutexe2x80x9d or xe2x80x9crelativexe2x80x9d values thereof in the physiological media. It is noted that operational characteristics of the optical probes and optical imaging systems of the present invention incorporating any of the solution schemes disclosed in the above co-pending ""972 application are only minimally affected by the number of wave sources and/or detectors and by geometric configuration therebetween. Therefore, unless otherwise specified, the optical imaging systems of the present invention may include any number of wave sources and/or detectors arranged in any geometric arrangements, subject to the xe2x80x9csymmetry requirementsxe2x80x9d of the co-pending ""972 application which will also be discussed in greater detail below.
As used herein, a xe2x80x9chemoglobinxe2x80x9d or xe2x80x9chemoglobinsxe2x80x9d mean either or both of oxygenated hemoglobin and deoxygenated hemoglobin. The xe2x80x9chemoglobin,xe2x80x9d xe2x80x9chemoglobinsxe2x80x9d or xe2x80x9cvalues of hemoglobinsxe2x80x9d represent properties of such xe2x80x9chemoglobins.xe2x80x9d Examples of such properties may include, but not limited to, amount or concentration thereof, total amount or concentration thereof (which corresponds to the sum of each amount or concentration of the oxygenated and deoxygenated hemoglobins), and the like.
xe2x80x9cChromophoresxe2x80x9d mean any substances in a physiological medium that can optically interact with electromagnetic waves transmitting therethrough. In general, such chromophore may include solvents of a medium, solutes dissolved in the medium, and/or other substances included in the medium. Specific examples of such chromophores may include, but not limited to, cytochromes, enzymes, hormones, neurotransmitters, chemo- or chemical transmitters, proteins, cholesterols, apoproteins, lipids, carbohydrates, cytosomes, blood cells, cytosols, water, hemoglobins, and other optical materials present in the animal or human cells, tissues or body fluid. Such xe2x80x9cchromophoresxe2x80x9d may also include extra-cellular substances which may be injected into the medium for therapeutic and/or imaging purposes and may interact with electromagnetic waves. Such xe2x80x9cchromophoresxe2x80x9d may include, but not limited to, dyes, contrast agents, and other image-enhancing agents, each of which may be designed to exhibit optical interaction with electromagnetic waves having wavelengths in a specific range.
xe2x80x9cElectromagnetic wavesxe2x80x9d as used herein generally refer to acoustic or sound waves, near-infrared rays, infrared rays, visible light rays, ultraviolet rays, lasers, and/or rays of photons.
xe2x80x9cPropertyxe2x80x9d of the chromophores refers to intensive property, including their concentrations, a sum of such concentrations, a difference therebetween, and a ratio thereof. xe2x80x9cPropertyxe2x80x9d may also refer to extensive property such as, e.g., volume, mass, mass flow rate, weight, volume, and volumetric flow rate of the chromophores.
The term xe2x80x9cvaluexe2x80x9d is an absolute or relative value which represents spatial or temporal changes in the property of the chromophores.
xe2x80x9cDistributionxe2x80x9d means two-dimensional or three-dimensional distribution of the values of the chromophore or their properties. The xe2x80x9cdistributionxe2x80x9d may be measured or estimated in a spatial, temporal, and/or image domains.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood and/or used by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be applied and/or used in the practice of or testing the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present application, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
Other features and advantages of the invention will be apparent from the following detailed description and from the appended claims.